Rails - Feb 2007 - method_missing in a AR child only catching 1 of several call

Hello -

Why does a view including the following fragment:

     <% for column in User.content_columns %>
       <td><%=h user.send(column.name) %></td>
     <% end %>

and the User model having the following defined:

     def method_missing(meth_id, *args, &blk)
       meth_name=meth_id.id2name
       puts("Calling: #{meth_name}")
       super
     end

only result in the following output of one method call when there are
several columns/attributes in the users table:

     Calling: name

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On 2/11/07, Aakash Chopra
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> Hello -
>
> Why does a view including the following fragment:
>
>      <% for column in User.content_columns %>
>        <td><%=h user.send(column.name) %></td>
>      <% end %>
>
> and the User model having the following defined:
>
>      def method_missing(meth_id, *args, &blk)
>        meth_name=meth_id.id2name
>        puts("Calling: #{meth_name}")
>        super
>      end
>
> only result in the following output of one method call when there are
> several columns/attributes in the users table:
>
>      Calling: name
Hi Aakash,

ActiveRecord::Base defines read methods lazily.  That is, until you
call a method to read an attribute, the method won''t exist.  Call a
method to read an attribute, and it''ll hit AR::B''s
method_missing
hook, which defines all the read methods, and hence, subsequent calls
to read methods won''t trigger method_missing.  You can witness the
effect in script/console:
>> Thing.instance_methods(false)
=> []
>> Thing.new.name
=> nil
>> Thing.instance_methods(false)
=> ["id?", "name?", "name", "value",
"value?"]

I''m not sure what you''re trying to do, but if you explain it,
someone
might be able to find something that works.  :-)  (Assuming this is a
problem for you.)

Regards,
George.

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George Ogata wrote:
.
.
> I''m not sure what you''re trying to do, but if you explain
it, someone
> might be able to find something that works.  :-)  (Assuming this is a
> problem for you.)
> 
> Regards,
> George.
Hey George - Thanks for the quick response.

I''d like intercept all method calls to my models accessing an attribute
in order to implement an attribute level authorization scheme - similar 
to the J2EE analog which is a pain but works (specified in ejb-jar.xml).

I think I found a way to configure rails to not generate the ENTIRE 
method list lazily - but the implication is that I''ll loose on 
performance:

config.active_record.generate_read_methods = false (instead of the 
default value of true)

Anyone got any Ideas?

Regards,
Aakash

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On 2/11/07, AC CE
<rails-mailing-list-ARtvInVfO7ksV2N9l4h3zg@public.gmane.org>
wrote:
>
> George Ogata wrote:
> .
> .
> > I''m not sure what you''re trying to do, but if you
explain it, someone
> > might be able to find something that works.  :-)  (Assuming this is a
> > problem for you.)
> >
> > Regards,
> > George.
>
> Hey George - Thanks for the quick response.
>
> I''d like intercept all method calls to my models accessing an
attribute
> in order to implement an attribute level authorization scheme - similar
> to the J2EE analog which is a pain but works (specified in ejb-jar.xml).
>
> I think I found a way to configure rails to not generate the ENTIRE
> method list lazily - but the implication is that I''ll loose on
> performance:
>
> config.active_record.generate_read_methods = false (instead of the
> default value of true)
>
> Anyone got any Ideas?
Have you looked around at the existing model-level authentication
plugins?  I think some do attribute-level authorization.  e.g., [1].

If that doesn''t fly for you, I''m not sure what the best way to
do this
is.  Once you''ve generated the read methods, they''re available
via
ModelName.read_methods.  Perhaps you can override these.  I don''t
think that''s particularly watertight, though.  #read_attribute, for
example seems to pull things directly out of the @attributes hash
inside the active record instances directly rather than going through
the read methods.  Perhaps you could hook into the #[] method on this
hash, but that''s getting pretty nasty!

class ActiveRecord::Base
  def initialize_with_authorization_check(*args)
    initialize_without_authorization_check(*args) do |*args|
      class << @attributes
        def [](name)
          # ... authorization check ...
          super
        end
        def []=(name, value)
          # ... authorization check ...
          super
        end
      end
      yield(*args) if block_given?
    end
  end
  alias initialize_without_authorization_check initialize
  alias initialize initialize_with_authorization_check
end

(Totally untested.)

[1] http://perens.com/FreeSoftware/ModelSecurity/

George.

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